The invention relates to electrodes for use in an electrochemical cell or battery, for example a bipolar lead-acid battery.
It is known to make bipolar plate electrodes for this purpose from lead and lead alloys. Ideally the electrodes are very thin to reduce the size and weight of the battery but thin sheets of lead metal and lead alloys are difficult to seal around the edges. A reliable seal is required in bipolar batteries to prevent conductive paths of electrolyte being formed from one side of the bipolar plate to the other, which would cause self discharge of the battery. The plate electrodes are not entirely resistant to galvanic corrosion which generally results in through-plate porosity in the form of pinholes (and the electrodes are heavy if manufactured in greater thickness to overcome this problem). Proposals to reduce the effective weight of the lead include the use of porous ceramics with lead infiltrated into the pores (which need to be of fairly thick section to be mechanically robust, and are thereby still rather heavy); and the use of glass fibres and flakes coated with lead, lead alloy, or doped tin oxide, or lead oxides as conductive particulate in a thermoplastic resin matrix but such electrodes are complex and expensive to produce. Carbon based materials have been tried, but most forms are susceptible to electrochemical oxidation.
Plates made exclusively of the Magneli phase suboxides of titanium (of the general formula TinO2n-1 (where n is an integer greater than 4 or greater) satisfy many of the criteria above. However, they are expensive to make, are brittle, and do not easily accept surface features, for example to accept and retain the battery paste coating.
We realized that plates can be made from the Magneli titanium suboxide material in particulate form in a suitable polymeric matrix, most, if not all, of these weaknesses can be overcome.